This invention relates to arrangements for controlling the engagement and disengagement of the differential lock and four wheel drive mechanisms of a vehicle.
Agricultural tractors conventionally comprise a back axle to which large diameter wheels are attached, these wheels not being steered, and smaller front wheels, which are steered. The rear wheels generate the main tractive force. On some tractors there is no provision to drive the front wheels, their only purpose being to steer the tractor. Other tractors are provided with steerable front wheels which are, or can be, driven.
This invention relates to tractors having front wheels, which may be driven. These tractors are well known to those skilled in the art as four-wheel drive tractors. The invention particularly relates to those four-wheel drive tractors where drive to the front wheels is selectively engageable and disengageable.
Agricultural tractors are usually provided with a differential lock in the back axle for reasons which are well known to those skilled in the art. Four wheel drive tractors are usually provided some form of differential in the front axle.
It is known to provide electro-hydraulic control systems, which engage and disengage the four-wheel drive and/or differential lock at the flick of a switch. In more complicated control systems sensors engage and disengage the four wheel drive and/or differential lock automatically to ensure the optimum and safe performance of the tractor.
In many countries of the world there is not the requirement for, or the ability to maintain, complex electro-hydraulic control systems, and there is therefore a need for a simpler means to control engagement and disengagement of the four wheel drive and/or differential lock.
It will be understood that whilst the invention is described with reference to an agricultural tractor, it is not limited to use with such a vehicle. The invention may be used with any four-wheel drive vehicle where two or four-wheel drive may be engaged/disengaged, and one or more differential locks which may be engaged/disengaged.
The invention provides an arrangement for selectively actuating the four-wheel drive and differential lock engagement means of a vehicle, the arrangement comprising a hand operable selector mounted in mounting means, the mounting means including a pathway, wherein the selector which co-operates with the said pathway, and wherein movement of the selector in a first direction from a first position to a second position actuates four-wheel drive, and further movement in the first direction from the second position to a third position actuates the said differential lock, characterised in that the pathway prevents the selector from moving in the first direction from the second position to the third position without first being moved in a second direction.
The selector may comprise a protrusion which co-operates with the pathway. The protrusion may comprise a lever, or a bracket.
The mounting means preferably comprises a bracket.
The selector may comprise a shaft mounted in the said mounting means, and the shaft may have a handle attached thereto.
Preferably, the shaft is mounted in the mounting means to move in the first direction axially, and in the second direction to rotate about its own longitudinal axis. Movement of the shaft in the second direction may be confined to rotation through an angle ().
The arrangement may further comprise biasing means to bias the shaft against movement in the said second direction, and the said biasing means may comprise a spring.
Advantageously, the four-wheel drive and differential lock engagement means comprises a hydraulic valve, and the arrangement comprises a valve actuator, and connecting means to connect the valve actuator to the selector. The connecting means may comprise a rod, one end of said rod being attached to the selector, the other end being attached to the valve actuator. The valve actuator may comprise a pivotally mounted lever.
Preferably, at the selector end the rod is attached to a bracket extending from the shaft of the selector.
The invention also provides a tractor comprising an arrangement for selectively actuating the four-wheel drive and differential lock engagement means of the said tractor.
The invention provides an arrangement for engaging the tractor""s four-wheel drive and differential lock, which is simple to manufacture, operate, and maintain. The arrangement is also inherently safe, insofar as the operator cannot engage the differential lock without taking a positive decision to do so, i.e. he must twist the handle before he can lift the handle upwards to engage the differential lock. The selector is biased into the safe position.
The invention can be used to engage or disengage one or more differential locks.